In that case the scene needs to be cut into subobjects.
Theoretically the .ASE format can support an infinite amount of polys, but each subobject only supports ~10,000 polys.
Chop the map in an organized fashion into elements—say "River", "Circle Wall 1" "Ground", etc, and convert them into the .ASE format. In the case of Sketch-up there are a few solutions, such as converting to .OBJ and using another program to convert to .ASE, or install a script plugin for direct conversion to .ASE.